1. Field of the Invention
The present invention relates to the transport of data, and more particularly to the collection and distribution of data wirelessly and bidirectionally.
2. Description of the Related Art
While advances in communication technologies have enabled convenient, virtually instantaneous connections between individuals throughout the world, the primary beneficiaries have been citizens of developed countries with established telecommunication infrastructures. Outside the developed world, particularly in sparsely populated rural areas or poverty-stricken regions, such infrastructures are rare. Consequently, e-mail, the web and readily available telephone service remain unavailable in such areas. Significant improvements are unlikely in the near term, given the present lack of communications infrastructure, as well as the cost of installing and providing access to modern communications equipment.
One communication technology developed for the transmission of data in areas lacking Internet infrastructure utilizes radio links, such as short-wave, citizens band (CB) radio, and packet radio. A first radio terminal, such as a terminal node controller, typically communicates with a second radio terminal via a base station. Perhaps the most reliable form of rural telecommunications is the use of a two-way radio. These have provided many advantages in rural locations, such as allowing community members to communicate with traveling doctors for medical concerns. Moreover, each terminal (e.g., two-way radio) is typically more robust and has a lower cost than many other communication systems. Nonetheless, base stations for these radio links require large antennas, significant electrical power to run, and are costly to maintain. Further, these systems traditionally communicate at a low data rate, often resulting in difficult or infeasible transmission of large data files.
Another communication technique employed in developing areas is communication via satellite terminals, such as a very small aperture terminal (VSAT) or an Iridium satellite data terminal. Satellite terminals can be deployed anywhere in the world without the need for preexisting infrastructure. Moreover, satellite terminals may provide reasonable data rates (e.g., 10 sec of Mbps for transmissions from the satellite to a ground station and 100 seconds of Kbps for transmissions from the ground station to the satellite). The satellite terminals, however, typically employ costly equipment which require uneconomical service charges. For instance, each ground station can cost $10,000 and may have service charges reaching several thousand dollars per year. Further, conventional satellite terminals require significant electrical power to operate and are not traditionally portable.
A low-cost alternative to the above-mentioned communication techniques that can be applied to developing regions utilizes telephone dial-up connectivity. Although conventional terminals having telephone dial-up capabilities are inexpensive and do not need much power to operate, the installation of telephone lines to developing regions is costly and, particularly in remote rural areas, frequently impractical. Further, since telephone dial-up communication capabilities require large infrastructure, lines may be installed only in certain areas, and even where installed, the lines may not be adequately maintained and often are too noisy to support electronic data transport. Conventional telephone lines typically enable low to medium data transfer rates (e.g., 9600-56000 bps).
Cellular telephone networks are often more realistic for developing, rural areas, since less physical infrastructure is required. Such networks are typically robust, flexible, scalable, and the cost of handsets is relatively low. Further, wireless technology eliminates the installation and maintenance costs of traditional phone lines. With the use of digital data protocols (e.g., time-division multiple access (TDMA) or code-division multiple access (CDMA)), these networks can transmit data in addition to voice. The expense of setting up a cellular infrastructure, however, often hampers the deployment in sparsely populated or poor developing regions. For example, installing a single cell can easily cost $100,000 and one cell typically provides only a few square miles of coverage. The economic status of developing regions frequently does not justify the expense associated with the implementation of a cellular infrastructure.
Instead of cellular network technology, systems such as wide area networks (WANs) and wireless fidelity (WiFi) networks use a packet-switched Internet Protocol (IP) to communicate data wirelessly. These networks support numerous devices, such as a wireless card used in laptops and specialized telephones (e.g., Voice Over IP). For long-range data transport, these systems employ powerful long-distance point-to-point radio towers that beam data from one village to another, or from an Internet connection point, such as an Internet service provider (ISP), to a local village. While such networks are attractive for use in modern cities, the infrastructure and maintenance needed to enable these communications is frequently too costly or impractical to enable widespread deployment in developing areas. Further, as such areas may lack electricity, the placement of the data transceivers are often constrained to particular locations having sufficient power or a sufficient power generator.
In order to reduce costs and reduce power consumption, the data rate of a WAN can be reduced. However, if the distance between towers is large (>10 km), this approach remains difficult to scale to many nodes and is susceptible to interference (e.g., radio frequency (RF) interference) between towers.